A 12" cabinet building project!

I am interested in building some cabinets, but my skills are limited. I have a mental block where math is concerned, and I have an uneasy relationship with computers, so I read up and tried to plot out the novice path to design. Reading most of the available texts was not the way for me, because I could not understand them, and they seemed to get way too deep into electrical/mechanical/acoustic engineering. It also seemed troubling that it wasn&#8217;t easy to figure out if I was reading about hi-fi, auto, or musical instrument speaker design.

Fortunately, I stumbled onto some of Bill Fitzmaurice&#8217;s posts. BFM seems to be setting the right course for me, as he provides what looks like high-end guidance that is still accessible to musicians. (My only affiliation with BFM is satisfied customer.) I ordered some of the plans from his site to get started. The panel jig plans were a great help, since I have a cheap table saw which is pretty exciting to use. The Tuba 30 and Omni 12 looked just about right for my purposes, but I wanted to check my box building protocols before attempting to build the horns on those designs.

I had most of a 4&#8217; x 8&#8217; sheet of &#189;&#8221; oak veneer plywood sitting in the shop that was left over from a furniture project. I didn&#8217;t need it for anything else, and I wasn&#8217;t sure if it would be void-free enough for a serious effort, so I decided to use it to build a few vented direct radiators to experiment with. I also wanted to start getting a feel for what the response curves I was seeing in my Eminence Designer software actually sounded like.

I chose to use Eminence Designer software after my attempts to download and run WINISD failed. My computer is pretty old, and doesn&#8217;t seem to be running properly, so this is not a comment on the software. I flailed around in there with my pathetic computer skills until I decided $70 or so for ED might be worth it.

The Eminence Designer software is easy enough for me to use. After entering the speaker&#8217;s T/S specs, it offers suggestions for a maximum output design, a hi-fi design, and an extended bass design. I entered the Eminence Delta 12LF specs and compared the response graphs for the three different versions.

I could easily see the difference in bass response between the three different size boxes using the graphs and the F3, but I couldn&#8217;t tell what that would sound like, how different the little bumps on the left side of the graphs would sound to me as a bass player. I decided to build the max volume and hi-fi sized boxes because I could use the plywood I already had, and while there would be some Kentucky windage in my first efforts, they would get me started on translating the response graphs and F3&#8217;s into audible examples. I needed to know what they would sound like, and how much the bottom end response and overall tone would benefit from the additional size of the hi-fi box.

I tweaked the shape of the boxes from ED's "Golden Ratio" and I tweaked the sizes slightly to fit the plywood I had on hand, so these are not the exact dimensions ED coughed up, but they are close. The first box has Vb of 1.7 cu. ft., Fb of 40 Hz, and F3 of 65 Hz. The larger, &#8220;hi-fi&#8221; version has Vb of 2.7 cu.ft., Fb of 42Hz, and F3 of 54 Hz. (For sake of comparison, the extended bass suggestion offered a Vb of 4.5 cu.ft., Fb of 38 Hz, and F3 of 45 Hz, all numbers rounded.) I braced the smaller box with a shelf brace, and the sides of the larger one with 3&#8221; strips of plywood, running lengthwise about 1/3 of the way across the panels. The larger box also has a front-to-back brace. The braces are all &#8220;swiss cheesed&#8221;, and all of the sharp edges were radiused with a router. The small box will get heavily dampened, the larger one will get typical damping.

In addition to the Delta 12LF's, I&#8217;m going to use an Eminence Alpha 8MR in the larger box, crossed over at 800 Hz, and three 3&#8221; vents, 6.7&#8221; deep. The smaller box will get an Eminence APT-80 tweeter, since I am pretty much out of room in there, and the Alpha 8MR won&#8217;t fit! The 4&#8221; diameter port will be about 7.2&#8221; deep. The baffles are &#190;&#8221; Baltic birch.

When I started planning, I was using the Bergantino HT 112 as my target. The convenience of carrying one lighter weight 1x12 when that would suffice, and two 1x12's when I needed to was very attractive to me. Your 2.1 cubic foot/driver box volume looks pretty good to me in terms of size, but I wanted to build a larger one as well so I could get a feel for how much bass I was sacrificing by using the smaller box. Eminence Designer recommends 4.5 cubic feet per Delta 12LF for their "extended bass" suggestion! I'm not that concerned about the size of the box, but I would like to stay a little smaller than that!

Here are some photos. I think you get the idea of the bracing, etc. They are painted in Vanderbilt Gray Duratec II. The hardware will be black and the grill cloth will be oxblood. I'll start with carpet and tolex coverings after I get the tone dialed in!

Thanks a lot for the suggestion. I went ahead and ran the Omega Pro 12 through Eminence Designer. Their "extended bass" suggestion specifies a 1.98 sq. ft. box, with an Fb of 37 Hz, and an F3 of 69 Hz. It takes a pretty large (min. about 4" dia.) and long (c. 8 1/2") vent, and Va gets critical (greater than 34 m/s) at a hair below 40 Hz, which might be a problem for 5 strings, right? Would a shelf port work better in this small (internal dimensions of c. 25 x 15 x 9 1/2) box? ED doesn't offer any help on this type of port, and I gather from other threads in this forum that calculating dimensions of a shelf port is different from other rectangular shaped ports because one wall of the cab also acts as a vent wall.

It hits F6 (if there is such a thing) at 47 Hz. It looks like it might need need some help on the other end, as the high frequency response tails off by 6 db at a hair over 1K Hz. An Alpha 8MR would probably fit in there, crossed over at 800 Hz.

Overall, the frequency response of the Omega Pro 12 seems to be a little more steep, with a more pronounced peak, than the Delta 12LF alternatives, but until I start testing these things I can't translate that into musicality! The Omega Pro 12 seems to provide better bass response than the Delta 12LF in a similiarly sized box, and obviously better power handling capacity. In the larger boxes, the Delta 12LF seems to provide extended bass response over the Omega Pro 12 in its 1.98 cu.ft. box.

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Here is the 1.7 cu. ft. box. It got heavily stuffed. Fb of this box with the 4" round port, 7.2" deep, is about 39.8 Hz, and the F3 is about 65 Hz. The second picture shows them both.

The comparative performance of the two cabinets, loaded with Delta 12LF's, should help me to start getting a handle on what the numbers and graphs translate into musically. Since they have different mid/tweeter arrangements, I'm not going to connect the crossovers initially. I don't want the different mid- and high-end responses to interfere with evaluation of the different cabinet's bass responses. I'm going to do some careful A/B-ing with different heads, four- and five-strings, and fretted and fretless basses so I can get a good idea of how much of a size compromise I can live with on the bottom end.

Attached Files:

The comparative performance of the two cabinets, loaded with Delta 12LF's, should help me to start getting a handle on what the numbers and graphs translate into musically. Since they have different mid/tweeter arrangements, I'm not going to connect the crossovers initially. I'm going to do some careful A/B-ing with different heads, four- and five-strings, and fretted and fretless basses so I can get a good idea of how much of a size compromise I can live with on the bottom end.

The Duratec II was a very satisfactory finish, for the cost and work involved, Crockett-man. It is water-based and it tends to "clot" pretty quickly in the tray, so you have to work fast. It provides a very evenly textured surface, and looks almost professional for a quick job with a roller. It also appears to be very tough. I painted these boxes before I cut the baffles, so I had to force the baffles in and out of the front recess a few times before I got the right fit. I figured I would have to touch up those inside lip surfaces, but they stood up to some considerable scraping without showing any wear. I've been told they clean up with a damp rag to like-new appearance, and because the surface is textured you can touch them up with a $ .25 acid brush and get them back to like new condition.

Another tip from Bill Fitzmaurice that paid off well for me. I don't like to keep gushing about that guy, but in the interest of telling the whole truth all the time, I can safely say almost all the brain power here was copped from him.

I decided to build the grille while I let all the adhesives inside the box cure. I hadn't done this in years, and I wasn't sure how much clearance I needed to allow so the frame would fit snugly inside the baffle cavity after the grille cloth was installed. I decided to put some music on while I figured it out. I grabbed a disc at random. It was Wham!'s "Make It Big".

I looked at the picture on the front, with the two guys and the pouty lips and hair and the arched eyebrows, and I became nauseous. I ran to the bathroom and puked.

I cleaned myself up, loaded the disc, and went back to work. I decided to use 1/2" Baltic birch plywood for the frames, rather than fumbling around with 1x1" or 2x1" strips. The difference in cost was minimal, and the single piece of plywood would make a sturdier frame. If the 1/2" depth doesn't provide enough clearance for the drivers, I will use 1/4" or 1/2" rubber feet for spacers. After cutting the outer profiles and the inner openings, I did a quick and dirty radius job on all of the edges with a drum sander chucked in a hand drill. Wham! was still playing, but with the saws and drill roaring, I hadn't heard much of it, so I started it over.

"Wake Me Up Before You Go-Go" kicks it off. There is a line about Doris Day in there, and there is an excellent bass player. I am surprised they gave the bassist so much latitude with the fills. He/she kills. Maybe it had something to do with the fact that there was no guitar on the track. I am starting to get interested, so I turn it up. None of the musicians are credited on the liner.

I wanted to get the size right before painting the frame. I was trying to figure out how to check the fit of the frame before installing the cloth. "Everything She Wants" came on. It sounds like a synth bass on this track, and it is perfect. It isn't like Stevie Wonder's synth tracks, but it is really good. I think I will place an ad to see if anyone has a keyboard to trade for one of the basses I don't play since I converted to MTD's.

I cut the frames for the grilles about 1/4" to 5/16" smaller than the cavity where the grille will be installed. I cut pieces of grille cloth about 1 1/4" larger on all sides than the frames. I laid the cabs on their backs, and laid the cloth over the top edges. The cloth is stiff enough that it stayed somewhat suspended over the baffle.

I lined up the frames over the cloth, still aligned over the baffle cavity, and gently pressed the frames down into the cavity. The frames pressed the grill cloth flat and firmly down against the baffles, and held it in place. The cloth is held tightly enough that I can adjust it perfectly straight inthis position. It holds the cloth in position so that after I prime and flat black the frames, I can staple the cloth to the back of the frame in this position, and get a nice straight, tight installation, pretty quickly. The photos give you the idea.

This trick seems like a useful one. It seems a lot more foolproof than trying to keep the cloth straight on the frame while both are lying on a flat surface, sliding out of alignment, and making me angry and frustrated. And I owe it all to Wham! Who ever would have thunk it.

I'm going to listen to Roy Haynes' "Birds Of A Feather" now, with Christian McBride, to get myself straightened out. Tomorrow morning the A/B process begins, using no tweeters or mids, and a Bergantino EX-112 as a reference.

My camera seems to shift colors in some random pattern that I haven't figured out yet. Plus I dropped it on a cement floor the other day.

The color is called Vanderbilt Gray, or maybe Vanderbilt Grey. I think it will look good with the oxblood grille cloth. Some of the best sounding vintage Fender guitar amps had that oxblood grille cloth, and being a sometimes guitar player, I had to try it out.

I think gray is more practical for something that gets dragged and bumped around. I don't think it will show the abuse as much as black, for instance. My black carpet-covered cabs look disgusting, picking up all kinds of garbage and filth everywhere they go. I think the garbage and filth will not be as obvious against a gray background.

Is it just me or did the cabs change colour somewhere along the line? No matter, it all looks good.

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i gotta say, the earlier pics of the grey cabs dont look ANYTHING like the cream colored cab with oxblood grill you just posted!!!
that being said, i am smitten with that cream color/oxblood, and gotta say that your cab looks like million bucks.

The metal grilles have a lot of advantages. I didn't want to spring for the full-frontal perforated panels on these cabs because I'm mostly interested in testing the bass response with the different size boxes, and I suspect the grille cloth is more transparent than metal alternatives. I was thinking of doing a "T.V." front cab someday, with tolex or carpet wrapped over a solid front, rear mounted drivers, and round metal covers over the driver openings. That would be pretty bullet-proof.

A lot of those treasured vintage Fenders had cream tolex and oxblood grille cloth. They looked fantastic. They rarely hit the market anymore because the guys that own them won't let them go. I found a place locally that sells a million different grades and colors of tolex-type stuff. I think I'll try the cream in the future. They also have a very rich-looking alligator pattern tolex...My amp could match my boots.

Finding those corners and structural extrusions that slot together makes tolex and carpet look a lot easier to apply. The extrusions and corners will cover most of the seams, which always gave me trouble in the past. I think doing up a professional looking cab will be achievable now.

Now if they will only sound right, I will be happy. In a few hours, a couple of disspassionate, objective bass players will be showing up, and the testing will begin.

Attached Files:

I wired up the woofer in the smaller cab the other day. I fired up my GK RB400-III and gently started to run it down. The handles vibrated like mad around a few frequencies in particular, primarily the G on the G string at the twelfth fret. The buzz seemed to be coming from the spring-loaded part of the handle itself, rather than the grip of the handle resting against the side of the cab.

The port tube I used was an "adjustable" four inch model. I don't think I got a stable enough bond when I glued the extension to the base, and that seemed to be humming as well.

I took the handles off, and glued up and installed a new port tube. That seemed to eliminate (most of) the unwanted resonances. I was surprised that those handles acted like that, considering that a lot of folks must buy them to install on speaker cabinets. I can't eliminate operator error.

This setback has delayed the serious testing, but my initial impression of the smaller cab is pleasant surprise. At low to moderate volume, it seems to be handling the lowest notes reasonably well. It doesn't seem terribly efficient, based on the amp's volume settings, but serious testing is yet to come.

Has anyone else had this problem with the smaller, flush-mounted spring-loaded handles?

That's a symptom of inadequate bracing. I try not to have more than 8 inches of unbraced panel width, if not less, and to have handle mounting screws go all the way through the panel and into a brace. If the box is vibration free the handles will be also, but if not they will let you know about it.

That's my thoughts too. Cab vibrations are a waste of acoustic power. Keeping them to respectable levels is very important to the overall system performance.

I have a test for this which is a little bit of fun. I place the cab on a wooden floor (wood on wood = no grip) and play a CD through it. I make sure the song has a big kick drum, and gradually bring the volume up. If the cab starts dancing across the room, then the cab needs more bracing.

Bracing is often missing from commercial cabs. Apparantly if makes construction too labour intensive, so instead they use thicker panels. IMO this is an unnecessary addition of weight. From my experiments, I believe 12mm ply which is braced has more rigidity than 15mm or 18mm ply which is unbraced. Guess which one is lighter!